1. Technical Field
The present invention relates to a receiver circuit that receives signals via a transmission line with a bus configuration.
2. Related Art
In related art, a communication system is known that transmits signals using a transmission line with a bus configuration. In this communication system, an impedance mismatch may occur at ends of the transmission line or at connecting ends of nodes on the transmission line. If such an impedance mismatch occurs, signals are reflected between these ends of the transmission line. The reflection resultantly induces ringing by which signals are permitted to repeatedly propagate on the transmission line. This causes oscillation in the signal waveform. Further, the ringing may cause distortion in the waveform of the transmission signals.
This waveform distortion chiefly occurs at an edge at which the signal level changes, and then converges with time. However, when the waveform distortion does not sufficiently converge before the timing of judging the signal level of bits, the signal level may be erroneously judged.
In particular, the communication system mentioned above is often configured to use a driver (e.g., a transistor having an open collector configuration) for the transmission of signals. This driver has output impedance that greatly changes between the time when a high-level signal is outputted and the time when a low-level signal is outputted. The communication system configured in this way may seriously suffer from waveform distortion at an edge where the output impedance changes from low to high.
A well-known approach for reducing such erroneous judgement of a signal level provides a configuration in which a resistance is connected in parallel with a terminating resistor for a predetermined time interval at the edge timing when the signal level of the transmission line changes. With this approach, the impedance of the transmission line is lowered to thereby prevent the occurrence of ringing and further the occurrence of waveform distortion (e.g., see JP-A-2001-127805).
However, the impedance of a transmission line varies depending on the length of the transmission line or the number of nodes connected to the transmission line. For this reason, the amount of resistance applied to a transmission line for the effective prevention of ringing varies depending on systems. Moreover, in a system in which nodes can be added on, the conditions of the system may alter after the nodes are added on. Therefore, the approach based on the related art raises a problem that a sufficient effect of preventing ringing is not necessarily ensured.
Thus, in order to sufficiently prevent the influence of waveform distortion, it has been necessary after all to limit the routing scale (the number of nodes, the length of wiring, the number of branches, etc.) or the communication speed.